Processing of color photographic materials generally comprises color development and desilvering as essential steps. In the color development step, silver halide exposed to light is reduced with a color developing agent to produce silver and, at the same time, the oxidized color developing agent is reacted with a color former (coupler) to form a dye image. In the subsequent desilvering step, the silver produced in the color development step is oxidized with an oxidizing agent called a bleaching agent and then dissolved by a silver ion complexing agent commonly called a fixing agent to thereby provide a dye image only on the color light-sensitive material (i.e., color photographic material or color photosensitive material.
The desilvering step includes two-bath desilvering steps which is effected by using a bleaching bath containing a bleaching agent and a fixing bath containing a fixing agent, and monobath desilvering step which is effected by using a bleach-fixing bath containing both the bleaching agent and fixing agent.
Actual development processing of the color light-sensitive materials further includes various auxiliary steps for maintaining photographic and physical qualities of an image or for improving image storage stability, such as hardening, stopping, stabilization, and washing.
With the recent increase of over-the-counter processing service systems used at small-sized laboratories, it has been keenly demanded to reduce the time required for processing so as to rapidly serve of customers. In particular, a reduction in desilvering time that accounts for the majority of the overall processing time has been strongly desired.
Various improvements, such as a combined use of a bleaching accelerator, have been made in the desilvering step. These have not yet been satisfactory, since an (ethylenediaminetetraacetato)iron (III) complex salt, which is a bleaching agent currently used in a bleaching or bleach-fixing solution, has an essential disadvantage of weak oxidizing power.
On the other hand, bleaching agents known to have strong oxidizing power include potassium ferricyanide, bichromates, ferric chloride, persulfates, and bromates. Each of these bleaching agents, however, involves disadvantages from the viewpoint of environmental conservation, safety on handling, and corrosion of metals, so that they are excluded from wide application in over-the-counter processing.
Of the known improvements, a bleaching solution containing a (1,3-diaminopropanetetraacetato)iron (III) complex salt and having a pH of about 6 as described in the example of JP-A-62-222252 (the term "JP-A" as used herein refers to a "published unexamined Japanese patent application") exhibits higher oxidizing power than the bleaching solution containing an (ethylenediaminetetraacetato)iron (III) complex salt, making it feasible to conduct silver bleaching more rapidly.
It is also known in the art (i.e., JP-A-62-222252) that the optimum pH level of a bleaching solution containing an aminopolycarboxylic acid iron (III) complex salt is around 6 from the consideration of a balance between assurance of a bleaching speed and prevention of poor color restoration of a cyan dye. That is, from the fact that a reduction of pH brings about an increase of bleaching speed but, in turn, induces poor color restoration of a cyan dye, a pH of about 6 has been regarded to be the optimum level and thus widely employed in the art.
A (1,3-diaminopropanetetraacetato)iron (III) complex salt has the problem that since they are strongly oxidizing, if a bleaching solution containing them is carried over into the subsequent fixing bath, it reacts with components in the fixing bath and causes fluctuation in the fixing solution's performance.
More specifically, in cases where a thiosulfate is used as a fixing agent, it is necessary to add a sulfite in order to inhibit production of sulfur through decomposition of the thiosulfate, but a (1,3-diaminopropanetetraacetato)iron (III) complex salt having a strongly oxidizing power reacts rapidly with this sulfite. As a result, the thiosulfate is liable to be converted to sulfur and the sulfur produced gives rise to the problem that it constitutes a hindrance by adhering to the film, etc. This problem becomes even greater if the amount of the (1,3-diaminopropanetetraacetato)iron (III) complex salt is increased in order to speed up processing.